Photometer



- Julyso, 1940.

J. H. GOSS El' AL PHOTOMETER Filed. Dec. 17, 1938 Inventors W Su cwm GW o www SKA C .l anw/m. JMJNT PW ,A

Patented Juy 30, 1940 yPiiTlinwT orner.

PHOTOMETER James H. i Goss and Francis K. McCi-lne.'

Swampscott, Mass., assignors to General Electric Company, a corporation of New York Application December 17, 1938, Serial No. 246,390

Claims.

An object of the present invention is to provide a photometer having a construction which combines the light-sensitive member and the'current measuring device into a compact, portable and inexpensive unit. Another object is to provide an improved photometer which is simple in design and construction and hence, one which lends itself to quantity production. 'Other objects are to provide a photometer which oiiers the maxi* Vmum utility, not only from the standpoint of measuring light coming from many directions but also from the standpoint o f greateraccuracy in aligning the light-sensitive surface with respect toa particular direction of` light; to provide va photometer which has-the maiimum amount of light-sensitive surface `for la given size of electrical measuring instrument to which the cell is connected and consistent Withthe practical and usable location of the cell; to provide a construction in which the cell is supportedby resilient means, in which the parts of the photometer may be easily and quickly assembled, in which it is unnecessaryto make any electrical connections after assembly, and in which the cell may be tested and theV current measuring device may be tested and adj with portions broken away in order to show the i Vinner construction. Figure 3 isa fragmentaryY View in perspective of the embodiment of Figures l and 2 with the'interior of the casing exposed and with sections cut through various walls of the casing, and Figure 4 is an elevation largely in sectionA showing the apparatus as seen from the right looking in the direction of the arrows 4-4' in Figure "2. Like reference characters are e utilized throughout the drawing to designate like 5 parts. y In the embodiment of our invention illustrated in the drawing'there is a casing il of a rectangufiar conguration and preferably made of a phenolic condensation product, such as Bakelite for example. As shown in Figures 2, 3 and 4, the casing is hollow and is provided at one end, the upperV end as shown in these figures with a rectangular compartment indicated atl2. The compartment is partitioned oi from the remainder or main portion of the casing by a wall ,or a shelf I3. An inwardly extending lip or flange I4 is provided for a purpose which will be explained presently. The front part of the casing, as shown in Figures l andv 4 is provided with an opening o I5 of any suitable shape, for example, rectangular as illustrated, and the'back of the casing is entireLy open at the time the casing is molded. Thus there are three openings in the casing at three different faces, the front opening, the top rectangular opening, and the entire ,Jack of the casing. A casing of this sort maybe readily molded on machines o1 standard design, infact, those machines which are .employed to mold the casings of voltmeters and ammeters may be 30 readily modified to mold the casing which has been descri' cd.

. Witinn the main part ci the casing ii, there is a microammeter, indicated broadly by the reerence numerai ia, of 'any'suitable f-.vell-J 3- d mounted in a' manner reine" e insV` nent is with a a @operating sca-ie face marked in :foot candles or similar indici further description of the instrument it s to necessary other than to state that it is provided with a zero correction mechanism i9 or" any suitable type and the zero correction mechanism i9 is att'ne end of the instrument shaft toward the back ,of the instrument instead of toward the front, in order that zero adjustment may be made and checked before assembly of the photometer, as will be explained hereinafter, and in order to permit using a casing 5G having less depth from frontrto back. In response to a voltage impressed across the terminals of the instrument ILS, the indicating needle or pointer il traverses the scale tace i8 and comes to rest at a position whichindicates a certain number-of 5 type is employed and preferably the type which has been described and claimed in the co-pending application of Clarence W. Hewlett, Serial No. 716,677, filed March 2l, 1934 and entitled Photoelectric cell and manufacturing processes therel0 for. Such a cell has been illustrated in Figures 2, 3, and 4 and is contained within the compartment I2 of the casing. As stated in the Hewlett application referred to, the cell consists essentiallyof Aa plate 20 of rectangular configuration and fabricated of a base metal such as iron or nickel. The plate is rst ground olf to make it smooth and clean, and .then sand-blasted, in order to give the light-sensitive material 2l (see Figures 3 and 4) a good grip on the surface. This work is of coursedone before the plate is assembledin the casing. ,The plate may then be mounted in any standard form of vacuum chamber and selenium evaporated in a high vacuum and condensed on the sand-blasted iron surface to form \the light sensitive layer 2|. The plate is then heated slightly iabove theA melting point of selenium and the condensed layer melted. The

plate may then be quickly cooled in an oven at a temperature of approximately 185 C. and held l at this temperature for a period of 24 to 72 hours,

the exact time of which can be determined by experiment and depends to some extent upon the initial quality of the selenium employed.

The selenium-covered iron plate is thereafter placed in an evacuated chamber, preferably containing argon at a pressure ofabout 200 microns `and a thin film 22 of a metal belonging to the second group of ,elements appearing in the,Meny delejeif Periodic Table, s uch as cadmium; i's'sput- .40 -tered on to the selenium, employing a sputtering current o f about 50 milliamperes.A The sputtering effect is preferably carried out in short ashes so as to'avoid heating the selenium surface unduly.v

During .the sputtering process, a flask of liquid air is arranged to cool the -sputteringchamber so that any condensable vaporsmay be immediately removed from the discharge. l

After the layer of cadmium or. similar metal has been deposited on the selenium, the plate is A removed from the chamber and laid aside in the air to age until the current sensitivity of the coated plate comes down to practically zero,at which time the electromotive force generated by the impingement of ambient light Aon the cell increases rapidly. `The aging step is terminated when the electromotive force-reaches a maxi- The cadmium-selenium-coated plate is again placed in the chamber containing argon and a very thin film 23 of platinum or -other non.

oxidizable metal sputtered on top of the cadmium,

the thickness of the platinum being exceedingly thin and just barely v'sibleon the surface.

.For the purposev of closing the opening at the back of the casing' II and for removably supporting the instrument I6, a back plate'` 24 is provided which may be composed o f the same material as the remainder of the casing Il. The back plate 24 is so dimensioned as to t within the bottom wallcf the casing Il, as shown at 25, but t0 extend upward as high as any portion of the casing. A flange or lip 26 is formed in the back plate 24 corresponding to the lip I4'which runs along the remaining three sides of the-top opening in the casing II. The top and back openings of the casing Il are thus continguous before the back'plate 24 is'in place. In order that the back plate 24 may besecured by means of screws-without applying excessive pressure to the material of which the back plateis composed, and for other purposes which will appear hereinafter, an additional back'plate 21 composed of metal is provided which ts outside the molded back plate 24. The back plate 24 serves as a base for the instrument I6 which is secured thereto in a conventional manner before the photometer as a whole is assembled.

Before the back plate 24 carrying the instru- -ment I6 has been secured to the casing II, the

coated light-sensitive plate 20 is mounted in the compartment I2. In View of the fact that the casing is open at the back during assembly the coated plate may be slipped into place readily into the compartment I2 with the ends of the plate resting in the grooves formed between kthe Shelves I3 and flanges I6. It will be observed that the upper and lower surfaces ofgsaidY grooves are formed by the lower surface-of the flanges I4 and the upper surface of the shelves I3, respectively, which surfaces are parallel to the top and bottom walls of the casing Il. As shown in Figures 2, 3 and 4 a conducting member 28 is positioned above the top surface of the coated plate 20. The conducting member 28 may be of any suitable shape, such` as to make electrical contact with the top surface of the light-sensitive coated plate 20, i. e.,

the top of theplatinum layer 23. -For example, v

the mernber28` may be a rectangular frame of the same outside size as the plate 20 in the form of a perimetrically complete punching which extends all along the edge of the top surface of the coated plate. For use as an electrical terminal vthe light-sensitive device firmly in place, there may be provided a spring strip 3l which bears at each end lagainst the ledge or shelf I3 and at the middle against the bottom surface of the plate 20. It will be understood thatthe spring strip 3l is y bowed' with the ends curved downward. For the purpose of providing a second electrical terminal l for the light-sensitive plate or cell 20 a backwardly projecting tab 32 is formed also in the spring strip 3| which is composed of conducting material, such as metal. The tabs or terminals 29 and k32 however are offset, or. occupy diierent positions along the back of the photometer for reasons which will be explained.A

In placing the light-sensitive member in position, it has been found that the most practical VWay is to assemble the coated plate, the conducting frame, the glass plate and the spring together and while holding the spring in a -iiattened position, to sandwich the assembly into the compartment I2, after which the'for'ce on thespring may -be relased, and the glass plate -30 will bear snugly against the inner surface' of the flange I4.

The instrument I6 is provided with terminal strips 34 and 35 laid in suitable channels 36 and 31 formed in the inside surface of the back plate 24. The channels 36 and 31 are not of uniform depth but are stepped to have increased depth at the upper ends 3B and 39, as 4shown in Figure 3, the deepened channel. portion 39 being shorter than the deepened portion 33. The upper ends 'of the light-sensitive device a backwardly projecting tab 29 is formed in the conducting frame 28;

of the lterminal strips v34 and 35 are correspondingly bent and the lengths of the offset* portions 40 and 4I are made the same so that when the terminal strips are resting in the channels 36 and 31 at the lowermost position possible, by reason of the lower limits of the deepened upper portions 36 and.39, the tip 4l of the terminal strip 35 will project upward further than the tip' 49 of the terminal strip 34, the diierence indistance of upward projection being such'as to correspond to the difference in height of the terminal tabs 29 and 32 of the light-sensitive device 20. The lattab 32. The vertical kpositioning of the tabs 29 and 32' and of the upper ends of the tips 49 and- 4I of the terminal strips 34 and 35 are such that.

the tip 4I extends upward far enough to make contact with the tab'29, and the tip 40 extends upf ward far enough to make contact with' the tab 32, but does not project therebeyond a distance as great as the thickness of the iron plate 20. Fur-` thermore, the terminal strips 34 and 35 are composed of spring material and are slightly bowed. particularly at the end portions 49 and 4i with the tips biased toward the tabs 32 and 29, so that the tip 4I can contact the light sensitive plate 20 only at the top surface to which the tab 29 is connected, and the tip cancontact the plate' 20 only at the lower surface to which the tab 32 is electrically connected. In this way short circuiting of the light-sensitive device by thetterminal strips .34 and 35 is -prevented evenfin cases where owing to inadvertence in manufacture the terminal tabs 29 and 32 should be absent or be of less than specified length.

After the various ,parts of the photometer have beenassembled the metal back plate 21 is placed against the molded back plate 24 and secured to the casing I I by means of suitable screws, such as the screws 42, for example,cooperating with suitable molded-in nuts, not shown, located at the bottom of screw holes such, as the .screw holes 43.

The terminal strips 34 and 35 are held in place in the channels 36 and 31 by the instrument magnet 16a which is fastened to the back plate 24. Preferably a sheet of insulating material I6b is interposed between the .magnet i6a and the back plate l21 and strip 35..' lThe strip 34, however, may be grounded to the magnet I6a at I6c (Figs. 3 and 4) The instrument movable coil (not shown) may also be grounded at one end to the 'magnet I6a by a connection through the instrument shaft and one of the.`spiral biasing springs I9a. The other end o f th`e instrument coil, however, is connected through an insulated spiral |917, in a manner well understood to those skilled in the art to a conductor I6d, soldered to the lower end of the termin Strip 3.5.

,In operation, the improved p otometer may be placed in a positionv with respect to .the'light source to be measured so that the light impinges.` Von the light-sensitive unit through the plate glass 30, and the position that the needle takes up along the scale will tell at a glance the intensity of light reaching the cell and whether or not the light is of'sumcient purpose at hand. i

It win be understood that with the instrument I6 connected to the light-sensitive device Y2t, the

intensity for the 3 zero adjustmentof the instrument I6 considered independently cannot be veried so long as there isa possibility of light falling vupon the cell 20 or of current being generated thereby. Accordingly the apparatus is so constructed that the light-sensitive device 20 may be tested'in the casing without the instrument I6 and the elec-r trical calibration of the 'instrument may be checked before assembly in the casing vIl without anynecessity for disturbing electrical connections or the cell 29 after the photometer has been assembled.

The zero adjusting mechanism I9 is placed at the back portion of the instrument and an plate 24 .for'receiving the slider 46. 'I'he slider .46 has an inwardly extending projection 49 .for

'engaging the forked arm 45 and an outwardly extending projection )49 which may be engaged by a thumb nail of the operator utilizing the photometer. 'I'he metal reinforcing the back plate 21 is'provided with a vertically elongated slot 50 for exposing the projection 49 of the zero .adjusting slider 46 and the plate 21.serves to hold the slider 46 in its groove 41. The plate 21 may be embossed or engraved to carry suitable tables, such as the recommended illumination levels foi` various types of work and other data, such as ,the trade mark of the manufacturer and the name of the apparatus and serves a multifold purpose as fa nameand information plate, means for-securing the zero adjusting slider 4 6 and means for reinforcing the .molded back plate 24. It is evident thatour improved photometer constitutes a compact and rugged structurev in which. the light-sensitive unit and the microammeter are adequately protected. by the casing Il and the glass member .30, .thus lending the device to rough usage, if necessary. It is also evidentl that if desired, the glass Amember may include, either as a separate element or by physicalV incorporation in the glass itself, a filter for 'determining the quality of light which is permitted to reach the light-sensitive surface. The

-dimensions of the photometer are relatively small. As giving some indication as to the compactness of the improved photometer,- a device has been made in which the dimensions of the n casing as measured across the scale face are '2% inches by 21A inches and the depth is' approximately 11A; inches. Such `'a device maybe readily carried around in the pocketv and has been found to register, in a practical manner,all light intensities, including daylight .and articial light.

the entire crosssectional area of the casing, the dimensionsof which are determined by the vsmallest size of a practical form of microammeteris utilized for the'purpose of riesy providing. as great a light-sensitive areav as is possible. Byv empioyingas large a light-sensitive area. for a given size o f casing as is-suilicient td accommodate a microammeter of practical .cle-

sig'n, the electromotive force generated by the.

light-sensitive member isl as large as possible under these conditionssothat the fznicroammeter responds in v.a very positive manner to any produced by for said instrument, a light-sensitive ldevice in light is propagated. It is apparent that the straight edges ofthe casing and the parallel cover for said casing and as a supporting vbase changes of electromotive force Y changes of light impinging on the light-sensitive plate form with oiset terminal tabs in electrical device. Moreover, in addition to offering the contact with the top and-bottom surfaces of said best design from' the standpoints of simplicity of lightsensitive device, means for supporting said design, ease of fabrication and also from the light-sensitive device along said top face so that standpoint of permitting the greatest amount of the device is externally exposed through the top light-sensitive area for a given size-of microamopening, the terminal tabs being toward the back meter, the rectangular design of casing lends itof said device, said instrument having a pair of self/to greater accuracy. in determining the direction and position from which the 'impinging cover and toward the top, one of said strips extending upward a greater distance, the difference being approximately that of the thickness arrangement'o the light-sensitive member with of said` light-sensitive plate, said further extendrespectv to the casing facilitate an accurate'aligning strip reaching the position of the terminal tab ment of the photometer with respect to any at the top surface of said light-sensitive-device, given direction of light, so that the direction the other stripreaching the position of the other in which the photometer is pointed is readily and terminal tab of said device, said instrument accurately determined when the photometer is being adapted to be placed in position by inser- I Letters Patent of the United States is;

, and back face of the casing, the opening at the said top face and supported by engagement with mitting insertion and removalv of said device, a

'electrical connections between said light-sensivstantially parallel to said top wall,` a light sensito be externally exposed through the opening tangular casing having openingsat three faces thereof conveniently designated as the front, top.'

'fs'.kcpesins'; a removable plate serving as a back held in the hand or is set down on adesk or against a wall.

In accordance withl the provisions of the patent statutes, I have described the-'principle of operation of my invention together with the apparatus which I now consider to represent the best embodiment thereof but I desire to have it underand electrical connections between said lightstood that the apparatus shown is only illustrasensitive device and said instrument lwill be made tive and that the invention may be carried out automaticallyby closure of said back wall. by other means. y 4. A photometer comprising a generally rec- What'we claim'as. new and desire to secure by tangular casing having openings at atleast two faces thereof, conveniently designated as the top and back of the casing, a cover for the back opening, an indicating instrument mounted upon said cover, adapted to be inserted through the back opening when the back cover is put in place and having 'a zero adjuster at the back portion thereof, supporting means extending. along the s ide walls of the casing from front to back in tion through the back opening and closure of said back 'opening by said backv cover, whereby the light-sensitive device may be tested sepainstrument may be tested and adjusted separately before being mounted within said casing,

l. A photometer comprising a generally rectangular casing having openings' at three faces thereof conveniently designated as the front, top

top face' being substantially coextensive with said face, an indicating instrument having itsdial visible through the opening in Vsaid front A face, supporting means extending along the side. 8 Plane SubStntialll/'fpal'allel t0 Said 120D face. walls of the casing from front to back in a plane a lighi'lrSeDSitiVe device having a P811' 0f terminal substantially parallel to said ,-,op face' a. light tabs projecting from one side thereof, means for sensitive device substantially coextensive with SIIDIJOrtingj. said light-sensitive device in abutment with-the top face of said casingy sothat the light-sensitive-device is externally exposed through the top opening, and the terminaLtabs extend toward the. back'of the casing, said instrument having a pair of terminal strips extending to the positions reached by said terminal tabs and adapted to contact said tabs, said lightsensitive device being adapted to be placed in position by insertion through` the opening in said said supporting means so as to be externally exposed through the. opening at such top face, said back opening extending to the top of the casing beyond said supporting/.means for percover plate closing said last-named opening, and

tive device and said instrument.

2.^A photometer `comprising a generally rectangular casing having openings in two walls thereof conveniently designated as the front and top walls ofthe casing, the opening in the top wail being substantially coextensive with said wall, an indicating instrument having its dial face visible through the opening inits front wall, supporting means extending along the side walls of the casing from-front to back in a plane subto be inserted through the back opening .when said opening is being closed bysaid cover, whereby an electrical connection is made through said terminal tabs when the casing is closed, and said be tested independently before assembly of said photometer. v ,5. A photometer comprising an -electrical instrument having a pair of terminal strips, a gentive devicesextending along. said top wall soas l least two faces thereof, conveniently designated in such wall, resilient means interposed between as the top and back of the casing andhaving a said light-sensitive device and said supporting pair of grooves 2111181151111salons4 the side walls ot means resiliently securing said light-sensitive 'e device against said to`p wall and electrical connections between said light-,sensitive` device; and said instrument. l l

' 3. A photometer lower projecting surfacesin a plane substantially parallel to said top face, a light-sensitive device comprising a ,generally recilt within said gr ves, a rectangularf' ame' of conducting mate al having a terminal/ tab extending' from one side thereof; said frame being of substantially the same size as said light-sensitive plate, a spring support of conducting sheet material having a projected area,`substantial1y and back facesfofjthe casing, an indicating instrument having its dial visible through the front terminall strips extending upward along the back Iately before insertion of the .instrument and the.

back face, and said instrument being adapted' instrument and said light-sensitive device mayerally rectangular casing having openings at at` the casing from front to back ,with uppernnd.

A 'in plate form having such lateraldimensig as to the same as the surface of the plate and having a terminalftab extending from one side thereof but offset lin position in relation to the terminal tab extending from said frame, said frame, lightlsensitive plate, and spring being mounted at the top wall of `said casing in said grooves with the said tabs extending toward the back of the casing and with the conducting frame above the light-sensitive plate and the spring( strip below it, said spring strip having its ends bowed downward abutting against the lower surfaces of said groove whereby said light-sensitive plate is firmly supported in said casing externally exposed through the openings in said conducting frame and in the top of said casing, said frame', plate,

and spring support as a unit being adapted to be placed in position by insertion through the -back opening, said instrument terminal strips being adapted to make contact with said terminal tabs.

6. A photometer comprising a substantially rectangular casing having at least two openings referred to for convenience as the top opening v:and the -back opening, a light-sensitive device -ing said last-mentioned ope secured in the upper portion to said'casing so` as to be externally exposed through said top opening, having a pair of .backwardly projecting terminal tabs, a back plate for closing said opening, an electrical indicating instrument securedA to said back plate and having a pair of terminal strips upwardly extending along the inner surface of said back plate, said strips being composed of electrically conducting spring material and being bowed inward and being. so positioned.

as to bear against said terminal tabs of the lightsensitive device when the back plate of the lcasing isV secured thereto, whereby the light-sensitive device and the instrument may be independf ently tested and the instrument may be adjusted -independently before assembly of the photometer,

7. In a photometer a generally rectangl-llar zcasing having openings at two faces thereof designated as the top and back faces of the casing, the'l opening inthe top being substantially coextensive with the topface, supporting means extending along the Vside 'walls-of the casing from front toback in a plane substantially parallel to said top face, a light-sensitive device in plate form substantially coextensive with said top face, a spring Vsupport in sheet formhaving substantially the sameprojected area as the surface of said light-sensitve device but bowed out of plane shape, said spring support being interposed between the lower surface of said light-sensitive device and the supporting .means along the side, walls of the casing, the ends of said springsup-- port being bowed downward whereby said lightsensitive device is 'resilientlysupported and externally exposed through theopening inthe top of said casing, said back opening extendinglto the top of the Vcasing beyond said supporting means for permitting'insertlonand removal ofV said light-sensitive device, and a cover plate clos- 8. In a photometer, a generally rectangular casing having a light admitting opening in one of the walls thereof, walls on either side of said said top wall, and a spring strip of substantially the same projected area as the surface of said iight-sensitive device, said spring strip being bowed with the outer ends downward and being mounted with its mid portion against the mid portion'of said light-sensitive device andv the lower ends abutting the lower surface of said grooves for resiliently securingv said light-sensitive device.

9. In a photometer, a casing having a wall with a light admitting opening therein substantially,

coextensive with the said wall, and walls on either-side thereof transverse thereto, supporting means extending along the side walls of the c'asing in ai plane substantially parallel to said first- .mentioned wall, a light-sensitive device in plate form substantially coextensive with said iirstmentioned wall, a spring strip of substantially the same projected area as the surface of said light-sensitive device but bowed out ofy plane shape, said spring support being interposed between the lower surface of said light-sensitive device and the supporting means along the side walls of the casing, the'ends of said spring sup' port being bowed downward whereby said lightsensitive device is reslliently supported and externally exposed through the said opening in the casing wall.

10. A photometer comprising a casing vhaving va wall with a light-admitting opening therein,

a light-sensitive device inplate :form substantially coextensive with said light admitting opening adapted to :dt against the inner surface of said wall around the lrim of the opening therein so as t-,be externally exposed through the opening, a spring strip of conducting4 material-having substantially the same projected area as the surface -of said ylight-sensitive device, said spring strip being bowed withI the outer ends inward` and being mounted withits mid portion against the mld portion ,of said light-sensitive device,

supporting means in said casing against which the outer ends of said spring strip are adapted to abut for resiliently securing said light-sensitrical contact with a portion of the outer sur- .face of vsaid light-sensitive device, an electrical instrument supported in said casing, andelec-n -trical connections from said instrument to said conducting strip and to said spring strip.

Jams 1H. Goss., Immers n MccUNE.

tive device, a stripof conducting material in elec- ,u 

